One approach to increasing palatability is through the addition of flavors and flavor-improving materials. For example, in U.S. Pat. No. 3,857,968 to G. J. Haas et al there is disclosed a process for improving the palatability of animal foods such as dog foods based upon a lypolytic and proteolytic enzyme treatment of a mixture of fat and protein. The exact reason for the improvement in palatability is not identified by the patent. It is disclosed that the reaction produces a complex array of reaction products which may be responsible for the improvement.
Amino acids are known to have widely varying aromas and flavors depending upon their type and concentration. And, there is nothing which indicates their inherent attractiveness to dogs. Thus, while U.S. Pat. No. 4,267,195 by J. Boudreau et al discloses that L-proline, L-cysteine, L-histidine, and L-lysine are taste active in the dog, there is an apparent need to balance the level depending upon the particular composition of the dog food.
A more general reference to the flavorful effect of amino acids is made in U.S. Pat. No. 3,653,908 to Buck et al which discloses an intermediate moisture animal food especially formulated for cats. While the reference indicates that acidic or enzymatic digestion of the food liberates flavorful amino acids, it is apparent from the conditions of processing that various reaction products of reducing sugars and amino acids are produced.
Further indicative of the effect of proteolytic digestion of proteinaceous ingredients of dog foods, is co-pending U.S. patent application Ser. No. 91,225 filed in the names of Franzen et al on Nov. 5, 1979. Therein, it is disclosed than an enzyme selected from the group consisting of ficin, trypsin, bromelain, pepsin, and papain produces a reaction mixture which, when combined with the other ingredients of a dog food, increases the overall palatability of the food.
It is also known that various sugars improve the palatability of dog foods. For example, U.S. Pat. No. 3,617,300 to Borochoff et al indicates that dextrose can improve the palatability of dog foods. According to the disclosed process, the starch content of a solid dog food is at least partially enzymatically converted to glucose by alpha-amylase and amyloglucosidase directly in the solid dog food. It was found that the combination of these two enzymes permitted the reaction to occur without adversely affecting the solid character of the dog food. In addition to the preparation of dextrose in situ such as by Borochoff et al it has been known for even longer periods of time to directly employ dextrose syrups which were prepared by enzymatically digesting corn apart from the other components of a dog food.
Thus, while progress has been made in recent years through the development of a variety of dog food palatants, there is a need for additional procedures and products which will yet further improve palatability.